What does it mean?
Much of the internal combustion engine’s power is lost as heat. For best performance, the engine needs to operate within a specific temperature range. Too cold, and the fuel does not vaporize as efficiently. Too hot, and the fuel vaporizes too quickly. Either situation can cause performance problems and possible engine damage. The engine cooling system is basically a coolant circuit between the engine and radiator, transferring a portion of combustion heat to the atmosphere.
Additional coolant circuits may include the heater core, for cabin heating, and the automatic transmission, to modulate automatic transmission fluid temperature. When the vehicle is cruising, usually above 35 mph, enough airflow is present through the radiator for efficient heat transfer. On the other hand, below 35 mph or when the air conditioner is running, more airflow is required. This additional airflow is provided by one or more fans, powered by drive belts or electric motors.
On some vehicles, the engine control module (ECM) monitors fan speed. This can be to confirm the fan is operating or to modulate variable-speed fans. If the ECM cannot detect a fan speed sensor (FSS) signal, it cannot determine fan operation or speed. In this case, it will illuminate the check engine light (CEL) and set a diagnostic trouble code (DTC). If there is no FSS signal, DTC P0528 is defined as “Engine Coolant Blower Motor Speed Sensor No Signal” or “FSS No Signal.”